Apparatus for removal of explosive gas from furnaces



Sept. 23, 1969 H. P. WILLETT APPARATUS FOR REMOVAL OF EXPLOSIVE GAS FROM FURNACES 5 Sheets-Sheet 1 Filed Sept. 20, 1967 FIG.

HOWARD P WI LLETT INVENTOR.

A G E N T Se t. 23, 1969 w T 3,468;104

APPARATUS FOR REMOVAL OF EXPLOSIVE GAS FROM FURNACES Filed Sept. 20, 1967 5 Sheets-Sheet 2 HOWARD P WILLETT IN VENTOR.

Sept. 23, 1969 H. P. WILLETT APPARATUS FOR REMOVAL OF EXPLOSIVE GAS FROM FURNACES Filed Sept. 20, 1967 5 Sheets-Sheet 3 F I G. 3

HOWARD P. W ILLETT ma /M1.

A G E N T Sept. 23, 1969 H. P. WILLETT 3,468,104

APPARATUS FOR REMOVAL OF EXPLOSIVEJ GAS FROM FURNACES Filed Sept. 20, 1967 5 Sheets-Sheet i 29 FIG.4

HOWARD P. W I LLETT IN V ENTOR.

AGENT p 3, l fi H. P. WILLETT 3,468,16

APPARATUS FOR REMOVAL OF EXPLOSIVE GAS FROM FURNACES Filed Sept. 20, 1967 5 Sheets-Sheet 5 FIG 5 HOWARD P. WILLETT INVENTOR.

BY QLJJ GENT United States Patent 3,468,104 APPARATUS FOR REMOVAL OF EXPLOSIVE GAS FROM FURNACES Howard P. Willett, Darien, Conn., assignor to Chemlcal Construction Corporation, New York, N.Y., a corporation of Delaware Filed Sept. 20, 1967, Ser. No. 669,010

Int. Cl. B01d 47/00 US. Cl. 55-222 11 Claims ABSTRACT OF THE DISCLOSURE An explosive gas is removed from the hood of a furnace such as an oxygen steel converter, by inserting an offgas removal duct into the hood and injecting an inert gas into the off-gas portion drawn off through the duct. The inert gas is injected into the off-gas at the inlet of the duct, together with a quench liquid, and the inert gas serves to dilute the explosive off-gas below the range of explosive mixture with air. The inert gas and quench liquid are introduced at the duct inlet by passing these streams through annular passages or pipes between the off-gas removal duct and external, coaxial or concentric ducts. In a cyclic furnace operation such as an oxygen steel converter, the duct assemblage is retracted from the hood during the pour and charge periods, and is reinserted during the oxygen blow period. The flow of inert gas may be terminated after the onset of the blow period, so as to remove off-gas undiluted with inert gas. The inert gas flow begins again towards the end of the blow period, when the duct assemblage is retracted from the hood, so as to prevent the induction of an explosive gas mixture into the duct.

BACKGROUND OF THE INVENTION Field of the invention The invention relates to the removal of off-gas from the air-ventilated hood of a furnace such as an oxygen steel converter, which generates a gas stream which forms explosive mixtures with air. The invention is more particularly concerned with the selective removal of an off-gas portion from the central region of the hood and undiluted with air, and with the prevention of the formation of an explosive mixture with air when this off-gas portion is removed from the central portion of the airventilated hood by the use of a selective duct or gas probe, which is inserted into the hood during periods of furnace operation when off-gas is being generated, and through which the off-gas portion is inducted for separate disposal.

Description of the prior art The conventional procedure in operation of many types of furnaces, particularly steel furnaces such as an oxygen steel converter or an electric furnace, involves a step or procedure in the operating cycle in which an off-gas is generated, which may be of a composition or contain certain constituents which form an explosive mixture with air in certain proportions. In the case of an oxygen steel converter, conventional operation involves a blow or melt purification step, in which oxygen or oxygenenriched air is injected into the furnace by means of an oxygen lance. The resulting furnace off-gas, consisting predominantly of carbon monoxide together with entrained solid particles such as iron oxide, is removed from the furnace through an upper outlet known as a mouth, and is collected in a gas hood. The hood surrounds the mouth of the furnace, however a spacing is generally provided between the hood and the furnace month, which 3,468,104 Patented Sept. 23, 1969 permits tilting of the furnace during the pour period and also allows air to enter into the lower annular portion of the hood.

An improved procedure for removing portions of the furnace off-gas from the hood is described in US. Patent No. 3,186,831. One of the problems encountered with this procedure, which involves the selective withdrawal of off-gas portions undiluted with air from the central region of the hood by means of a gas probe, is that explosions may occur in or adjacent to the probe or removal duct during portions of the cycle, particularly during the onset of the blow period, due to the formation of explosive mixtures of off-gas and air in the probe. The problem is encountered mainly when the gas probe or removal duct is retracted from the hood during the pour and charge periods, and when the gas removal duct or probe is reinserted into the hood prior to or during the blow period. In other instances, explosions may occur due to the mixing of the air, which enters the lower part of the hood about the furnace mouth, with the furnace off-gas being inducted into the centrally disposed inlet of the gas removal duct. It is generally considered necessary to induce a certain amount of air into the furnace hood for ventilation and combustion purposes, since if no air is inducted into the hood, some of the furnace offgas escapes into the atmosphere surrounding the furnace. This result is highly undesirable since the off-gas is usually poisonous or otherwise injurious to the health of personnel, as well as being inflammable and causing an air pollution hazard. The hood cannot be conveniently attached around the furnace mouth by a gas-tight seal because of basic process considerations, since the furnace must be tilted after the oxygen purification step. Typical details of hood arrangements and overall apparatus layouts are shown in US. Patents Nos. 3,002,739, 2,908,737, 2,862,701, 2,847,206 and 2,803,450. Other arrangements of otf-gas removal apparatus for various types of furnaces are shown in Switzerland Patent No. 198,255 and US. Patent Nos. 2,831,467, 2,855,194 and 2,093,666.

Summary of the invention ice In the present invention, an off-gas portion is selectively removed from the central region of the air-ventilated hood of a furnace, by means of an apparatus which prevents the possibility of explosions due to mixture of offgas with air, which in many instances may form an explosive mixture with the furnace off-gas. Many types of industrial furnaces generate an off-gas containing combustible constituents such as carbon monoxide, which may form an explosive mixture with air in certain proportions. The invention is particularly applicable to the removal of off-gas from an oxygen steel converter, which is operated with a blow period during which pure oxygen gas or a gas stream principally consisting of oxygen is injected into a bath of molten ferrous metal, so as to react with the carbon content of the metal and form an off-gas principally containing carbon monoxide.

The present invention provides a central duct which extends into the air-ventilated hood of the furnace and terminates at an inlet in the central region of the hood, for selective removal of off-gas essentially undiluted with air from the central region of the hood. A concentric coaxial annular duct, or two concentric ducts, are provided external to and coaxial with the central duct. In instances when two ducts are provided, inert gas such as steam or nitrogen is passed through the annular passage between the central duct and the middle annular duct, and the inert gas stream is discharged through central duct openings and into the furnace off-gas at the central duct inlet. This dilution of the furnace off-gas with inert gas serves to form a gas mixture which is non-explosive and may be safely induced through the central duct and out of the hood. A quench liquid stream such as water or a light hydrocarbon oil is passed through the outer annular passage between the middle duct and the outer duct, and quench liquid is thus projected through openings and transversely into the diluted gas mixture at the central duct inlet, to quench the hot gas mixture in order to facilitate removal and subsequent processing. In instances when the furnace off-gas contains entrained solid particles, the injection of the quench liquid will also provide gas scrubbing and solids removal, and the entrained liquid droplets subsequently removed from the off-gas will contain the solid particles removed from the off-gas during the quenching procedure. When only one annular duct is provided, the annular passage serves to conduct quench liquid, and a plurality of pipes are disposed within the annular passage to conduct inert gas to the central duct inlet.

In application of the present invention to cyclic furnace operations such as an oxygen steel converter, which has an oxygen blow period followed by molten metal pour and charge periods, the ducts assemblage is inserted into the hood at the onset of the blow period, with the flow of both inert gas and quench liquid being maintained during the insertion. During the actual blow period, when the ducts assemblage is positioned in the hood and the furnace is generating off-gas, the flow of inert gas may be terminated, so as to induce a concentrated furnace olf-gas undiluted with inerts into the central duct. At the termination of the blow period, the flow of the inert gas stream is resumed, and the ducts assemblage is retracted from the hood, to permit furnace movement or tilting during the pour and charge periods.

The principal advantage of the present invention is that furnace off-gas which forms an explosive mixture with air may be safely removed from the air-ventilated hood of a furnace, without the danger of explosion taking place either in the off-gas removal apparatus or during subsequent processing of the off-gas. Another advantage is that the device and apparatus may be installed in existing plants or installations, as well as in new furnace facilities. A further advantage is that the off-gas is simultaneously diluted and quenched at the point of induction into the off-gas removal duct, which prevents air which may enter the duct through the air-ventilated hood from forming an explosive mixture with the off-gas in the duct. In practicing the invention, the inert gas is injected into the furnace off-gas prior to the transverse injection of quench liquid. This is advantageous because greater gas volumes and fiow rates are provided during the transverse injection of quench liquid, which causes improved dispersion of the quench liquid into the combined gas stream. Another advantage of the invention is that the apparatus may be retracted from the furnace hood during portions of the furnace operating cycle. When the present invention is applied to oxygen steel converters, other advantages are obtained. During most of the oxygen blow period, the inert gas flow may be terminated, and the converter ofiF-gas consisting essentially of carbon monoxide together with metallic iron fume or dust is induced into the central duct in an undiluted state. This highly advantageous, since high purity carbon monoxide is produced, with negligible dilution due to air entrainment or inert gas injection. After processing for the removal of metallic iron fume, the off-gas is suitable for chemical usage such as in the production of hvdrogen or synthesis gas for methanol synthesis. In addition, the recovered iron fume is in the form of a valuable and nearly pure iron powder, since no air is induced to cause partial conversion to iron oxides. Finally, the facility of the present invention can be added to any conventional or existing BOF plant to improve air pollution control, and to permit increased oxygen blowing rates in some cases.

it is an object of the present invention to provide an 7 improved apparatus for removing furnace off-gas from the hood of a furnace or the like.

Another object is to selectively remove off-gas from the central region of the air ventilated hood of a furnace while preventing the formation of explosive mixtures of off-gas and air.

A further object is to inject an inert gas into off-gas being selectively removed from the air-ventilated hood of a furnace, to prevent the formation of explosive mixtures of off-gas and air.

An additional object is to provide an apparatus for injecting inert gas and quench liquid into an off-gas portion which is selectively inducted from the central region of the air-ventilated hood of a furnace.

Still another object is to provide an improved apparatus for dilution of furnace elf-gas with an inert gas, followed by transverse injection of a quench liquid into the gas mixture for cooling and scrubbing of the gaseous phase.

These and other objects and advantages of the present invention will become evident from the description which follows.

DESCRIPTION OF THE DRAWINGS AND PREFERRED EMBODIMENTS Referring now to the drawings,

FIGURE 1 is an elevation view of the apparatus of the present invention as applied to the removal of 01fgas from an oxygen steel converter,

FIGURE 2 is an enlarged view of one embodiment of the off-gas removal ducts assemblage,

FIGURE 3 is a sectional plan view of the apparatus of FIGURE 2, taken on section 3-3,

FIGURE 4 is an enlarged isometric view of an alternative embodiment of the off-gas removal ducts assemblage, and

FIGURE 5 shows a preferred mode of operation of the apparatus of the invention and treatment of the mixture of off-gas, inert gas and entrained liquid droplets removed via the central duct of the apparatus.

Referring now to FIGURE 1, the furnace 1, which is typically an oxygen steel converter, is provided with an inner lining 2, which will usually be composed of a refractory material. Furnace 1 has an upper mouth opening, which in the case of oxygen converters serves as a gas outlet as well as a charging inlet for impure melt and as a pouring spout when the furnace is tilted. When furnace 1 is operated as an oxygen steel converter, oxygen lance 3 is also inserted through the furnace mouth. Lance 3 serves to discharge oxygen or oxygen-enriched air into the melt which is contained in furnace 1.

A hood 4 is disposed about the mouth of furnace 1, and serves to collect the furnace off-gas stream 5, which in the case of an oxygen steel converter will principally consist of carbon monoxide, together with inerts and entrained solid particles such as iron fume. Hood 4 is spaced away from the outer wall of furnace 1, and ventilation air stream 6 is drawn into the hood. Air stream 6 serves to sweep oiT-gas stream 5 up into the hood 4 and prevents leakage of the off-gas into the surrounding atmosphere. The flow of gas stream 6 is highly important, since oif-gas stream 5 is generated and withdrawn at a highly elevated temperature, and as mentioned supra stream 5 consists mostly of carbon monoxide which is highly explosive when mixed with air in certain proportions. In addition, stream 5 is highly poisonous and contains a high dust loading, and cannot be allowed to escape into the surrounding air. Air stream 6 has another important function, since stream 6 sweeps up along the inner surface of hood 4, and thus serves to cool the lower part of the wall of hood 4. In addition, hood 4 is externally cooled by means of water jacket 7.

As air stream 6 rises within hood 4, contact between the air and ofl-gas stream 5 takes place. This results in combustion in the upper part of hood 4, and the oxygen content of stream 6 is consumed. A final gas stream 8 is withdrawn from hood 4, principally consisting of carbon monoxide, carbon dioxide and nitrogen, together with entrained solid dust particles. Stream 8 is subsequently cooled and treated by scrubbing or filter means, not shown, for removal of solids. The cleaned gas stream is then discharged to the atmosphere, since stream 8 has a very low heating value due to dilution with air stream 6.

Returning now to the lower part of hood 4, the ducts assemblage or gas probe unit 9 is inserted through or below the wall of hood 4, with the inlet of unit 9 located in the central zone of hood 4, where the gas composition consists primarily of off-gas stream 5 containing only a negligible proportion of air. Unit 9 is preferably inserted through the spacing between the lower end of hood 4 and the mouth of furnace 1, however unit 9 may also be inserted through a fitting in the wall of hood 4. A portion of off-gas stream 5 is drawn into probe 9, and as will appear infra this portion is immediately accelerated to a high velocity, diluted by the injection of an inert gas, and quenched and scrubbed by transverse injection of scrubbing liquid. The resulting diluted gas stream 19 containing entrained liquid droplets is drawn up through unit 9. This mixed stream now preferably passes through an entrainment separator such as cyclone 11, for removal of entrained liquid droplets and mist. The collected liquid, together with solids washed out of the gas stream, is removed from cyclone 11 via bottoms stream 12. Unit 11 may alternatively consist of the entrainment separator apparatus described in U.S. Patent No. 2,998,100 or other bafiled devices, or other suitable gas-liquid separation devices. The resulting gas stream, now free of entrained liquid droplets, is drawn out of separator 11 and through duct 13 by centrifugal blower 14. Other suitable types of blowers or gas impellers may be employed for this purpose. The resulting gas stream 15 is now discharged from the system via duct 16. Stream 15 is a clean cooled gas, consisting mostly of carbon monoxide plus inerts, and is suitable for usage as a heating fuel gas or for other purposes. In some instances, stream 15 may be employed in chemical manufacture or synthesis, such as in production of hydrogen by the water gas shift reaction.

The flow of quench liquid and inert gas streams into the ducts assemblage 9 is also shown in FIGURE 1. Stream 17, consisting of a suitable quench liquid such as water or a light hydrocarbon oil, is passed via pipe 18, valve 19 and pipe 20 into the outer annular passage in unit 9, and as will appear infra, stream 17 is projected transversely into stream 5 at the inlet of unit 9. Stream 21, consisting of a suitable inert gas such as steam, nitrogen, carbon dioxide or filtered flue gas, is passed via pipe 22, valve 23 and pipe 24 into the inner annular passage in unit 9, and is dispersed into the off-gas stream 5 at the inlet of unit 9 to dilute the off-gas and form a gas mixture in the central duct of assemblage 9 which is of a composition below the exposive range.

Referring now to FIGURE 2, one embodiment of the gas removal ducts assemblage 9 is shown in detail. The ducts assemblage is bounded by the upper flat ringshaped annular bafiie 25, from which the inner duct 27 depends downwards. The duct 27 is coaxial with the outer duct 9, and when the ducts 27 and 9 are cylindrical, these ducts will appear as concentric circles in horizontal cross-section, as will appear infra. A flat ring-shaped annular bafiie 29 is provided at the lower terminus of duct 9, and the baffle 29 extends inwards from the end of duct 9 to the lower end of inner duct 27. The pipes 24 extend into the annular passage between ducts 9 and 27, and then extend downwards to the terminal inert gas discharge openings 31 which are provided in the wall of duct 27 adjacent to baflle 29. A second plurality of openings 32 are provided in the wall of duct 27 above the openings 31 and connecting with the annular passage between ducts 9 and 27.

In operation of the apparatus of FIGURE 2, the inert gas stream 21 passes via pipe 22 and valve 23 to pipes 24. The inert gas flows downwards through the pipes 24, and is directed inwards at the lower end of the ducts assemblage and is projected through the openings 31 into the stream 5 of hot off-gas within the inlet of duct 27, thus serving to dilute the oif-gas to a non-explosive gas mixture. The mixture of off-gas and inert gas flows upwards through duct 27 and passes openings 32. The quench liquid stream 17 passes via pipe 18, valve 19 and pipe 20 into the annular pasage between ducts 9 and 27 and below bafiie 25. The quench liquid flows downwards through the annular passage between ducts 9 and 27, and is diverted by bafide 29, so that the quench liquid is projected through openings 32 and transversely into the mixture of hot off-gas stream 5 and inert gas streams 21, which is inducted at high velocity through central duct 27. The quench liquid thus serves to cool and scrub the gas stream. The mixture of off-gas, inert gas and quench liquid droplets flows upwards through duct 27 via stream 10 and is discharged via duct 9 for further processing as described supra.

FIGURE 3 is a sectional plan view of FIGURE 2, and ShOWs the arrangement of the pipes 24 within the annular passage between ducts 9 and 27, as well as the concentric circular arrangement of the ducts 9 and 27.

Referring now to FIGURE 4, a preferred embodiment of the invention is illustrated, in which the quench liquid flows through an outer annular passage to the central duct inlet, and is then reversed in flow path so that the quench liquid is transversely projected into the mixture of off-gas and inert gas. This arrangement is preferable in most instances, since greater dispersion of the quench liquid is attained due to higher gas velocities at the point of liquid injection, because of prior addition of inert gas to the furnace off-gas. The quench liquid stream 17 passes via pipe 219 into the annular passage between outer duct 9 and middle duct 26, and flows downwards past the flat ring-shaped annular disc bafile 33, which extends between the lower end of duct 26 and the central duct 27. The bafiie 33 is provided with a first plurality of spaced apart openings and a second plurality of spaced apart openings. A curved transfer pipe 34 extends between each of the first plurality of openings in baffle 33 and one of the openings 35 in the wall of central duct 27. The quench liquid stream flowing downwards through the outer annular passage between ducts 9 and 26 reverses its flow path around the lower end of duct 26, fiows into the pipes 34, and is thereafter transversely projected into the highly accelerated gaseous phase via openings 35. The inert gas stream 21 passes via pipe 24 into the inner annular passage between central duct 27 and annular duct 26, and next flows through the second plurality of openings in bafile 33, and through the plurality of curved pipes 311 which extend between the openings in baflie 33 and the openings in section 38. The section 38 may be a separate gas inlet section or duct, however 38 is preferably an extension of the central duct 27. The inert gas is discharged from openings 37 into the gas passage defined by section 38, and combines 'with the inflowing olfgas stream 5 to form a mixed gas stream of non-explosive composition, which is then quench-cooled and scrubbed by the quench liquid injected via openings 35 as described supra. The mixed stream of quench liquid droplets, offgas and inert gas is discharged from conduit 9 via stream 10 for further processing as described supra. Enclosure bafile 29 extends between the lower end of outer duct 9 and section 38, which as described supra may be merely an extension of duct 27 Referring now to FIGURE 5, the installation of the off-gas removal apparatus relative to an oxygen steel converter is illustrated in conjunction with off-gas processing for removal of entrained liquid droplets. The converter 1 holds a charge 40 consisting of molten ferrous metal.

Oxygen stream 39 is passed via lance 3 into the furnace or converter 1, and stream 39 is discharged above and into the liquid body 40 consisting of molten metal, with the resultant generation of off-gas stream 5 which rises together with annular ventilation air stream 6 into the flare skirt 41 of the hood 4. Some of the off-gas, together with products of combustion generated by reaction of stream 6 with portions of stream 5, is removed from hood 4 via stream 8. The off-gas removal duct assemblage 9 extends into the spacing between flare skirt 41 and the mouth of furnace 1, with the inlet of unit 9 being disposed in a central region below or within hood 4. A central off-gas portion 5 is inducted into unit 9, and quench liquid stream 17 and inert gas stream 21 are passed via inlet pipes 20 and 24 respectively into unit 9. The entire unit 9 assemblage is mounted on carriage 42, which is a wheeled on roller support which is movable so that unit 9 may be retracted from the hood region during metal pour and charge periods.

The mixture of furnace off-gas, inert gas and entrained liquid droplets passes from unit 9 as stream via flexible transfer conduit 43 into enlarged entrainment separation section 44, in which most of the entrained liquid is separated -out of the gas phase as liquid pool 45, which forms in the bottom of the curved section 44. The liquid separation section 44 may be provided with suitable bafiles, not shown, to aid in the separation of entrained liquid from the gas phase. The separated liquid, which will usually contain entrained solid particles removed from the gas phase, is removed from the bottom of unit 44 via outlet nozzle 46 as stream 47, which is passed to filter or settling vessel 48 for the separation of a solids or slurry phase which is discharged as stream 49. The clarified liquid is recycled from unit 48 as stream 17.

Returning to section 44, residual entrained liquid mist or droplets are removed from the gas phase by entrainment separator 50, which usually consists of a wire mesh unit. The separated liquid passes from unit 50 to pool 45, while the gaseous phase, now free of entrained liquid, passes to the inlet of blower or fan 51. Blower 51 discharges the gaseous phase to the bifurcated gas transfer section 52, from which the gas may pass either to atmospheric discharge via valve 53 and pipe 54 as stream 55, or to further utilization via valve 56 and pipe 57 as stream 58.

During the oxygen blow period as illustrated in FIG- URE 5, an off-gas rich in carbon monoxide is generated by unit 1, which in most instances must be recovered in a cooled, scrubbed and undiluted state. Therefore, after the onset of the blow period, with unit 9 in position within hood 4, the flow of inert gas stream 21 is terminated, since there is no danger of explosion of the rich off-gas being inducted via 5 into unit 9. Then the valve 56 is opened and valve 53 is closed, so that rich off-gas passes to further utilization via stream 58. At the termination of the blow period, the flow of inert gas stream 21 is resumed, valve 53 is opened and valve 56 is closed, and the diluted ofi-gas is discharged via stream 55. The carriage 42 is then displaced outwards and upwards, so that unit 9 is retracted from the hood 4. The flow of streams 17 and 21 may then be terminated, and blower 51 is turned off. The furnace 1 is then tiled for the pour period followed by a refill period when a fresh charge of impure molten ferrous metal is added to the furnace, and the furnace 1 is again disposed under hood 4. The blower 51 is started up again, to provide induction flow in unit 9, and the flow of streams 21 and 17 is resumed. Unit 9 is then reinserted in hood 4 for further induction of olfgas, without any danger of explosions during insertion due to the flow of stream 21. After the onset of the blow period with stream 39 flowing through lance 3 at a desired flow rate, the flow of stream 21 is terminated, valve 56 is opened and valve 53 is closed, to complete the operating cycle.

Numerous alternatives within the scope of the present invention will occur to those skilled in the art. The apparatus is applicable to numerous types of furnaces such as the various metallurgical furnaces which generate offgases which form explosive mixtures with air, such .as olfgas containing carbon monoxide, hydrogen or organic vapors. The inert gas is preferably added to the off-gas prior to injection of quench liquid, to promote greater dispersion of the liquid phase into the gas stream. In addition, the inert gas must be inserted into the inducted off-gas prior to injection of quench liquid to prevent any runoff or spillage of quench liquid into the converter. The quench liquid preferably flows through the outer annular passage between ducts 9 and 26, in order to promote cooling of the ducts assemblage by providing an in situ cooling jacket. The inert gas may be transported to the off-gas inlet by a plurality of pipes extending within the central duct to the inlet section and provided with appropriate discharge nozzles, and the quench liquid may be similarly transported to the off-gas inlet section. In this case, either or both of the annular passages and ducts would be omitted. The ducts 9, 26 and 27 are preferably cylindrical and coaxial, so that the ducts assemblage will appear as concentric circles in transverse section. However, square or rectangular ducts may be employed in some instances, particularly when a large proportion of the total furnace off-gas is to be removed by means of the ducts assemblage of the present invention and large gas flow volumes must be handled. In some instances, a plurality of duct assemblages may be provided for a single furnace hood, to provide withdrawal of elf-gas from different sections of the hood.

An example of an industrial application of the invention will now be described.

EXAMPLE The ducts assemblage and apparatus of the present invention as shown in FIGURE 4 was designed for application to an oxygen steel converter. During the blow period, about 566 standard cubic meters per minute of gaseous oxygen was discharged through the oxygen lance, with the resultant formation of about 1100 standard cubic meters per minute of elf-gas principally consisting of carbon monoxide. The off-gas Was generated at about 1400 -C., and about 550 standard cubic meters per minute of off-gas was inducted through the off-gas removal duct. The gas was quenched to C. using 1420 liters per minute of quench water as stream 17, which saturated the gas stream. The velocity of the off-gas in the central off-gas removal duct was 122 meters per second. About 600 pounds per minute of saturated steam was employed as the inert gas stream 21 for dilution purposes. The diameter of the innermost gas removal duct 27 was 46 centimeters, the middle duct 26 was 64 centimeters in diameter, and the outer duct 9 was 75 centimeters in diameter.

I claim:

1. An apparatus for removing a furnace elf-gas from the hood of a furnace, said off-gas containing a constituent which forms an explosive mixture with air, which comprises a first duct, said first duct extending into said hood and terminating at an off-gas inlet in the central region of said hood, means to induct an off-gas portion from the central region of said hood into said first duct, whereby said off-gas portion is accelerated to high velocity at the inlet of said first duct, a second duct, said second duct extending coaxially with and external to said first duct and terminating adjacent to the inlet of said first duct, said first duct being provided with a first plurality of spaced apart openings adjacent to the inner terminus of said second duct, means to pass an inert gas stream through the annular passage between said first duct and said second duct, whereby said inert gas stream is injected through said first plurality of openings and into said off-gas portion adjacent to the inner terminus of said second duct and said off-gas portion is diluted with inert gas to form a non-explosive gas mixture within said first duct, a third duct, said third duct extending coaxially with and external to said second duct and terminating adjacent to the inlet of said first duct, said first duct being provided with a second plurality of spaced apart openings adjacent to the inner terminus of said third duct, means to pass a quench liquid stream through the annular passage between said second duct and said third duct, whereby said quench liquid stream is injected through said second plurality of openings and transversely into said off-gas portion adjacent to the inner terminus of said third duct, thereby quench-cooling said off-gas portion, and means adjacent to the outlet of said first duct to separate entrained liquid droplets from the resulting cooled nonexplosive gas mixture removed from said first duct.

2. The apparatus of claim 1, in which a terminal disc bafile is provided at the inner terminus of said second duct and extending inwards between said second duct and said first duct, said disc bafile is provided with a first plurality of openings and a second plurality of openings, together with a first plurality of transfer pipes, each of said first transfer pipes extending between one of said first plurality of openings in said disc bafiie and one of said first plurality of openings in said first duct, whereby said inert gas stream is transferred and injected into said off-gas portion prior to the injection of said quench liquid stream, and a second plurality of transfer pipes, each of said second transfer pipes extending between one of said second plurality of openings in said disc baffle and one of said second plurality of openings in said first duct, whereby said quench liquid stream is injected transversely into the non-explosive gas mixture of said off-gas portion and said inert gas stream.

3. The apparatus of claim 1, in which said furnace offgas principally consists of carbon monoxide.

4. The apparatus of claim 1, in which said quench liquid is water.

5. The apparatus of claim 1, in which said inert gas is steam.

6. The apparatus of claim 1, in which said inert gas is nitrogen.

7. The apparatus of claim 1, in which said furnace is an oxygen steel converter.

8. The apparatus of claim 7, in which said combination of first, second and third ducts is retractable from said hood, and said ducts combination is retracted from said hood during the pour and charge periods of the operating cycle of said oxygen steel converter, and is reinserted into said hood during the blow period of the operating cycle of said oxygen steel converter.

9. The apparatus of claim 8, in which the fiow of said inert gas stream through the annular passage between said first duct and said second duct is terminated during at least a portion of the blow period of said oxygen steel converter, whereby part of said oif-gas portion is recovered substantially undiluted with inert gas.

10. An apparatus for removing a furnace olf-gas from the hood of a furnace, said olf-gas containing a constituent which forms an explosive mixture with air, which comprises a first duct, said first duct extending into said hood and terminating at an off-gas inlet in the central region of said hood, means to induct an off-gas portion from the central region of said hood into said first duct, whereby said off-gas portion is accelerated to high velocity at the inlet of said first duct, a first plurality of openings in the wall of said first duct, said first openings being disposed adjacent to the inlet of said first duct, means to pass an inert gas stream through said first plurality of openings and into the inlet of said first duct, whereby said inert gas stream is injected through said first plurality of openings and into said off-gas portion at the inlet of said first duct and said off-gas portion is diluted with inert gas to form a non-explosive gas mixture within said first duct, a second duct, said second duct extending coaxially with and external to said first duct and terminating with a fluidimpervious closure adjacent to the inlet of said first duct, a second plurality of openings in the wall of said first duct, said second plurality of openings being spaced adjacent to the inlet of said first duct and downstream of said first plurality of openings, means to pass a quench liquid stream through the annular passage between said first duct and said second duct, whereby said quench liquid stream is injected through said second plurality of openings and transversely into said non-explosive gas mixture within said first duct, thereby quench-cooling said nonexplosive gas mixture, and means adjacent to the outlet of said first duct to separate entrained liquid droplets from the resulting cooled non-explosive gas mixture removed from said first duct.

11. The apparatus of claim 10, in which said means to pass an inert gas stream through said first plurality of openings is a plurality of pipes, each of said pipes extending through the annular passage between said first duct and said second duct to one of said first plurality of openings, together with means to pass inert gas through said pipes for discharge into said first duct through said first plurality of openings.

References Cited UNITED STATES PATENTS 3,173,489 3/1965 Okaniwa et al. -60 3,186,831 6/1965 Pike 75-60 3,190,747 6/ 1965 Namy et al 75-60 3,215,523 11/1965 Richardson 75-60 REUBEN FRIEDMAN, Primary Examiner CHARLES N. HART, Assistant Examiner US. Cl. X.R. 55-228 

